Richard Branson and Boeing heap hope-and hype-on biofuels.

Aviation entrepreneur Richard Branson recently demonstrated what kind of leverage is available to an ecologically friendly and media-savvy billionaire. He did this, as he always does, by putting his venture capital where his mouth is.

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In April the CEO of Virgin Atlantic Airlines and Virgin Fuels agreed to buy at least 15 Boeing 787 Dreamliners, but the $2.8 billion-plus deal came with a catch: Virgin’s fuels division, Boeing, and General Electric had to form a partnership to test alternative fuels in 747s next summer. Last year Branson founded Virgin Fuels and pledged $400 million over three years for its renewable energy and efficiency projects.

Branson’s bold moves may quicken the pace of research to find environmentally friendly fuels for aviation. It is not a matter of will—airlines, airplane manufacturers, and military agencies all want to make aviation greener—but of engineering: finding a secure and more predictably priced fuel source and refining it to produce energy efficiently. The challenge is daunting; in the United States alone, about 60 million gallons of jet fuel burns each day.

Today, airplanes burn less gas per mile than ever, but Boeing predicts air travel will double by 2020. Aviation will have a much bigger effect on the environment, and incur much higher fuel bills, unless a source of alternative fuel helps shrink costs.

While airplanes are responsible for only about three percent of human-related greenhouse gas emissions (cars and power plants produce far more), scientists charge that the industry contributes six to 12 times more to global warming than the other sources. That’s because airplane emissions occur mainly at high altitudes, where greenhouse gases last longer, says Robert Hendricks, a scientist at NASA’s Glenn Research Center in Cleveland, Ohio, where the agency is working with the Air Force and others to investigate new fuels. Airplanes also leave contrails and cirrus clouds, which trap heat.

But which alternative energy source—soybeans, algae, leftover fat—is best? And can one sole contender fit the need?

Traditional aviation gas known as Jet-A, or the military version, JP-8, is some of the most prized stuff to be derived from a barrel of oil, the petroleum version of fine wine. It’s refined to almost pure hydrocarbon energy, packing more energy per pound than most other fuels. It also flows easily at the frigid temperatures of high altitudes and remains chemically stable—at low risk of explosion—at high temperatures.

Standard alternative fuels don’t stack up. Ethanol, for instance, packs far less punch: To get the same amount of energy, an airplane must carry about 65 percent more ethanol than jet fuel. The additional weight necessitates larger wings and engines, which in turn demand still more fuel. Then there’s biodiesel, which turns the consistency of Vaseline at cold temperatures. Liquid hydrogen isn’t a great option, because it has to be carried in heavy cryogenic tanks, a requirement that forces airplanes to burn more fuel to stay aloft—especially when groaning in slowly for landings.

Although an unmanned jet powered by a hydrogen fuel cell flew over Switzerland this year, today’s fuel cells—which generate electricity by combining the charged particles of hydrogen and oxygen—lack the power to run anything more than a small aircraft.

But Boeing has hopes of replacing the auxiliary power unit generators with more efficient fuel cells that produce little or no pollution, even when running on jet fuel, in order to power the electrical systems on commercial airplanes.